The software shows both a voltage and a “counts” value when selecting trip points for the analog
input. The “counts” value is a variable from zero to 255 (8 bits). If you have connected a 3.3K Ohm
resistor in series, and you want to select a trip point at, say 12V, you will ignore the voltage shown
by the configuration software, and simply select the correct counts value of 214. ((12 / 14) x 250*)
Please note:
The analog input counts never go above 250 (This is a known hardware limitation
problem) and the input is
NOT
isolated, and must be used with care.
5.12. Battery Input
The GSM Commander provides connections for an external rechargeable 12V battery. Under normal
circumstances, the GSM Commander will trickle-charge the battery at a current of about 60mA. In
the case of a power failure, the GSM Commander then starts drawing power from the battery to
continue operating.
In the case of a power failure, the GSM Commander can continue operating from the external
battery. The unit can be configured to perform certain tasks (like sending a warning SMS) if the
battery voltage falls below a certain point, and can also perform tasks in the case of a power
failure. (Like sending an SMS and switching on emergency lighting)
In cases where the GSM Commander is used in conjunction with a large system with its own battery
(such as UPS systems), the battery terminals of the GSM Commander can be safely connected to the
large (12V) battery, and the GSM Commander can then monitor the battery voltage for you (only
while power is NOT supplied to the power input connector).
Also, in cases where the user may want to connect other hardware directly to the battery, be aware
that this will probably drain the battery, since the charging current from the GSM Commander is so
low. Other hardware should rather be connected to the power terminals provided at the inputs
(See sec 5.8 for more information on this)
.
Internal to the GSM Commander, the Battery terminal is wired with a 47ohm resistor between the +
Batt terminal and the positive power supplied to the GSM Commander. There is a diode in parallel
with this resistor (cathode facing to the battery) to allow the GSM Commander to draw power from
the battery under power-fail conditions.
A resettable fuse has now also been added to give the Battery terminal added protection against
voltage spikes and short circuits.
Suitable batteries are available from
Polygon Technologies
.
5.13. Internal Battery
GSM Commanders with a "+" at the end of their part numbers (), are equipped with an
internal 3.7V li-ion battery. This battery can keep the unit going even when the mains power is
turned off.
Please Note:
Because of the low battery voltage, the GSM Commander will not be fully functional
when running from the internal battery. Specifically,
ALL
INPUTS and OUTPUTS will be disabled.
The GSM Commander will still be able send/receive SMSes and voice calls. This is very handy for
applications where the only requirement of a battery is for power failure notifications. Mounting an
external lead-acid battery can be troublesome. This option will effectively solve the problem.
Another area where this feature is important, is in security applications. Sometimes criminals would
break open the enclosure and cut all the wires in an effort to prevent an SMS or call from being
made. The internal battery will be impossible to turn off, and thus they cannot prevent the
transmission.
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